To build an image processing system by connecting a digital color copying machine (described as "copying machine" hereinafter) to a computer such as a personal computer or a workstation and also by using the copying machine as a scanner or a printer, it is necessary to connect a dedicated printer controller to a section between the computer and the copying machine. The configuration is employed because a copying machine is ordinarily designed to execute real time operations for reading and forming an image without storing the read image data once in a memory to read out the stored image data for forming the image later and is not adapted to transfer full-color image data requiring a large data volume to a computer.
For this reason, a printer controller has a configuration suited for connection with a copying machine, and has a CPU, a ROM, a RAM, a HD, an IC for communications or the like each adapted to the configuration, and further has an image memory for temporally storing image data read by a copying machine or image data to be printed by a copying machine. And the printer controller is connected to a copying machine via an image data bus of the copying machine and also connected to a computer via a general purpose communication line (such as SCSI).
The printer controller receives image data read with a copying machine and stores the image data once in an image memory, and can transfer the image data with communication via the general purpose communication line with a computer. The printer controller executes other types of processings, when PostScript data is received from a computer, such as converting the PostScript data to bit map data and inputting the data into a copying machine.
As described above, availability for various purposes is realized in connection with a copying machine by using a printer controller, whereby any type of computer can be connected to a copying machine. Further, it is possible to build a network by connecting a plurality of computer units via a printer controller to a copying machine.
By the way, when executing the processing of printing data for post card printing prepared by a computer on both surfaces of a post card form with a copying machine, a thickness of a post card form is larger than that of recording paper used by a copying machine or the like, so that it is impossible to print the data on both surfaces of the form with a double-side printing function of a copying machine due to construction of a transfer mechanism in the copying machine. For this reason, it is required to manually feed forms when data is to be printed on both surfaces of a form.
Namely, when printing data on both surfaces of a post card form, employed is a method in which previously prepared top surface data for a post card and rear surface data for a post card are inputted, the top surface data for a post card is printed on one surface of a post card manually fed, and then the post card form is turned over and again manually fed to print the rear surface data for a post card on another side thereof.
However, although the printer controller can provide wide range adaptability in connection between a computer and a copying machine, as the printer controller and a computer are connected with a general purpose line such as SCSI, for instance, in a case where full-color image data read from a document having A3 size with the resolution of 400 dpi is transferred to a computer, at least several tens of minutes is required to transfer the image data, which means that the transfer rate is disadvantageously low.
As a result, as it is not realistic to read image data at the high resolution of, for instance, 4000 dpi, generally image data is read at the low resolution of 200 dpi or below and transferred to a computer, so that it has been impossible to obtained high quality image data. Namely, a higher transfer rate can be realized only at the sacrifice of image quality. In addition, when image data is read at a low resolution, a data rate becomes smaller, which makes it impossible to remove moire generated when a printed matter is read, resulting in further degradation of image quality.
Also when outputting image data from a computer to a copying machine, it is difficult to print high quality images at a high speed.
In addition, to make it possible for a print controller to receive image data from or output image data to any type of copying machine, the print controller itself requires such components as a CPU, a ROM, a RAM, a HD, an IC for communication, an image memory, and for this reason the printer controller is disadvantageously expensive.
Further, in addition to the difficulty of printing high quality images at a high speed, when data for a post card is to be printed on both surfaces of a post card form with a copying machine, it is necessary to execute printing on both surfaces of a post card form manually feeding the form, and after the data is printed on one surface of the post card form, when the post card form is turned over and again manually fed to print data on another side thereof, it is required to ascertain a direction of form feeding so that the printing direction on one side is identical to that on the other side of the post card form. Especially, in a case where data for a plurality of sheets of post cards is to be printed on a post card form having the size equivalent to a plurality sheets of post cards, if an operator forgets to check the direction in which the post card form is fed, data printed on a top surface of the post card form mismatches that printed on a rear surface of the form, which makes the printing work very complicated and troublesome.